1. Technical Field
The present invention relates to a channel estimating method in a receiver device using Orthogonal Frequency-Division Multiplexing (referred to as “OFDM”) or similar Fast Fourier Transformation (referred to as “FFT” below) for demodulating, and to a channel estimator of the same. The present invention is technology applicable, for example, to an equalizer for full-seg Integrated Services Digital Broadcasting-Terrestrial (referred to below as ISDB-T), to an equalizer in OFDM, and the like.
2. Related Art
Up to now, for example as described in Japanese Patent Application Laid-Open (JP-A) No. 2000-115087, a channel estimator for deriving a delay profile of an OFDM signal (electrical energy against time delay, referred to below simply as “electrical energy”) derives the electrical energy, by: receiving a OFDM signal; demodulating by performing frequency conversion using fast Fourier transformation; then extracting a desired signal (called a Scattered Pilot signal in ISDB-T, referred to below as a “pilot signal”); and performing inverse fast Fourier transformation (referred to below as “IFFT”).
However, in channel estimators up to now, a noise component superimposed on the reception signal is included in the electrical energy, and not only is the noise component superimposed on the electrical energy present in the channel, but with the channel in time delays in which the electrical energy is extremely small, or maybe not present, electrical energy becomes evident due to the noise, and correct channel estimating results are not obtainable. If equalization processing is performed based on such incorrect channel estimating information and OFDM demodulating carried out, since equalization processing is performed with electrical energy infiltrated with noise this leads to the problem that the reception characteristics are impaired.
Recently in demodulators using non-OFDM signal FFT, of a single carrier having a guard interval (referred to below as “GI”) provided to prevent intersymbol interference due to multi-path delay, and other such devices, similar problems to the above also occur.